Solid state display screens



May 24, 1960 P. M. G. TOULON SOLID STATE DISPLAY SCREENS 2 Sheets-Sheet 1 Filed April 24, 1958 Fig.2.

INVENTOR Pierre MG. Toulon a/BY ATTOIRNEY WITNESSES May 24, 1960 P. M. ca. TOULON sour) STATE DISPLAYSCREENS Z SheetS-Sheet 2 Filed April 24, 1958 Fig.3.

Fig.4.

United States Patent SOLID S A E IS AY SC E Pierre M. G. Toulon, Turtle Creek, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed Apr. 24, 1958, $81. No. 730,669 8 Claims. Cl. 313-468) This invention relates to display devices and, more particularly, to methods of fabricating multielernentary solid state display devices. Recent'developments in panel type light amplifiers utilizing electroluminescent phosphors have given rise to the possibility of utilizing .such devices as a display screen. The various disadvantages and inadequacies of the conventional display transducer, the cathode ray tube, are well known. Prominent among those which are generally cited are the grossly inconvenient shape and size, limited brightness, and susceptibility to flicker.

The utilization of a solid state display screen utilizing an electroluminescent phosphor could foster advances in the electronic image systems which have heretofore been mp e y said i us ina equacies o he ode: ay tube.

In e Prior several Pro sa s hav b en made in u l zin n ele t n seent pho ph hich s sol wish d t een two ar a ot m tua l hemeho eo e condu t ng s r s for dis ay ng a s emed mage. th s ty e o s em. the ec r al xei ti n thy em t of th dis l y os he in h t m oi a ery sh r p se p ed n e e y home n h Pr -litperto me ee'oi ele hmin seeh materia i wo d. e pee that h s nd mil r h mes are ho pree eel'e d p a de es It i imh s hle to tmhs er shh e en ener y to the Phos hor h suc so, ar angement-t yield a qu te s een b i h ne In or to. u ilize e et o hmi se ee in a o eetieel. dis lay. it s hee ssa y o Pro e eans. by hi h the e i atio app ied to ea h e n o jor frac io of the fr me is p ce s is a e st a e. si ce i n ol es means for sto i g he c nt ol i n l th t s tst brig tness o the element for one or more frame periods.

n my e pe ng pp icat on S rial No; 727.916, filed April 11, 1958, entitled -1Display Systems," now US. Patent No. 2,875,380, there is disclosed a solid state display screen which utilizes nonlinear capacitors as, the

storage means in controlling the light from they electroluminescent phosphor. This type of display screen provides the obvious advantage. over conventional display of high brightness and minimum flicker. The one, disadvantage of the structure disclosed in the previously mentioned application is the complex nature of the control structure. In building these structures, it is necessary to provide one or more of these nonlinear capacitors for each light-producing element in the display screen. In a device like the conventional television system, the structure might require more than 250,000 elements.

The control structure which may consist of one or more capacitors performs the'same function regardless of the structure. The electroluminescent elementassociated with each control structure emits light in accordance with an alternating or time varying potential appearing across it while the nonlinear capacitor arrangement causes this potential to be altered in accordance with the applied video control potential.

Accordingly, the object of this invention is to. provide 2,938,135 Patented May 24, 960

a method and process of building such complex structures which are adaptable to mass production.

It is another object to provide an economical process and method of fabricating. a solid state display screen in which individual storage elements are provided for cash display element desired.

Itis another object to provide demountable typeunits which provide ease of manufacture and also ease in rem al an r placement in ca e of breakdown.

It is another object to provide a method of forming a structure in one uni fo app y ng Potentials to any gh producing screen.

These an ther o jec s are efieot by thisinven as will e app rent. fr m the fol owi g des ript taken in. accordan e with the ac ompanyi g dra inssthr u hout wh ike re ere c hara ters ndi te l k p s, ant n whic F ure l i a p rt a pe p et ve, sch matic view of a i p ay s en ma in acco ance w th the p ih pl s of my in e ion;

F g 2 th ou 4 ar per p c e v ws sho ng s p in the ormation of the display s r en s ru ur a ord- 't he ea h ng of my nve a d Fig- 5 s n enlarged pe sp t ve vie o a p r i n of h cont o s ruc re made i acc rdance i h the pr ent invention.

R i ring in etai t lie he e is o n a struct c nstructed in aeeor anee h he tea hing of my nht on he t u th e llus r ted in Fiat c ns s s a light tra mittin suppor m mbe l l hioh may e o gla s The. area f th pport member 1 would. h the size o the entire ereen o di nley devic D posite on Qli i'S lI' Q Q of the supnor inamemher leontiniiohs coati g llof a li ht t ansm t ng eleeti eallyeohdu tiv material. s ch s sta hi oxide. w ieh ser s as the fr m. ele trode oi t e sht emittihs. or Pr du i P rt on oi th scr e struc re Ahy ot r sui able ligh t a smi ting ma e ia h ng suita le eetrieal p perti s ay e util zed 7 eposit d. n electr ca ly conducti layer 1.2. is. h

1 co inuo s se n 1 a su table phosphor ma erial.

such z n sulfide, corner the the ssheseae iyat or zine sulfid opper acti ated, The phospho aye .1 m y he deposi ih any ui able. masher- Qne speci ic. m hod is to ut iz a finely d vid d Phospho material. uch a zin sul de o. i eted w opp adm xed with. a o ve sh h. s: hutyl a etat nd i h a. Poly i yl h oride lacquer. he Pr portio s i. the con ti uent a no e itiea nd may be ried. th hv wide limits, a sne i ie x mple. thr per shy weight of; phosph em ye mixe th 50 pa s y we gh of: hin er and: 3 nar svhy eigh of polyviny chlor e cque Th fore oin ad ixturem y be sp yed in a plura i y of. co ti s. or e ample four. a c d ng to..-the es ed; t ickness; a i-the Co tin d i etween each coa ng opera on.- Qthehdielee ries an s v nts m y be ubsti ut d r theforego hs: pe examp e as i well kno n.-

D po n. the xpos r-tote. o he pho ph ayer 1 i a mosaic coat n made p o pl rality o elem nta a ea 16 suitable e e tiee ly conductive ma rial. su h, as s l r a uminu The el ments. 16 r sepa ated; so o pr ide sui ab e nsulatio for a y voltages applied so as to provideseparately controllable gh -produ g lem n s. he nhmh rof. heon tiv leme ts 16 il d p n n he. amo mt o re oluti n an pl y elem n s d si ed n. h ima edewie e n:- ductive elements 16 which are the basis electrodes of th l gh -pr c ng cr m y he; depo i d; by e ap ta inset suit ble. mate ial hrough am h. as, is we l known in the art. The resulting s ructure. ma es a plu ality of separate co trollable llgh -pliql-I l illgifi. mea s Gt l l which are discussed more fully in an article entitled Electroluminesence and Related Topics" by G. Destriau and H. F. Ivey in the December 1955 issue of the Proceedings .of the I.R.E.

By way of explanation, electroluminescence was first ;completely disclosed by G. Destriau in London, Edin- .electrodes excites the phosphor material to luminescence, and the phosphor materials which display this electroluminescence are thus termed field responsive. Such phosphor materials are normally admixed with a dielectric material or a separate layer of dielectric material which is included between the electrodes in 'order to prevent any arcing thereacross which would short out the electroluminescent cell, but a separate dielectric material is only desirable and not mandatory for the cells may be operated under some conditions without any dielectric where the applied electric field is as high as '100 kv. per centimeter. Normally, the spaced electrodes are parallel, but they need not be, as where graded field intensities are desired.

A control or storage portion which includes a nonlinear capacitor is associated with each of the elements 16 to provide the desired control of the individual light cell in response to a video or control signal. The control portion of each display area or light-producing element of the screen in the specific embodiment shown consists of a bridge-type circuit utilizing two nonlinear dielectric capacitors connected in series. The center of :the bridge is connected to the back electrode 16 of the light-producing screen and the other leads of the capacitors are connected to two separate bus bars 18 and 20 for providing the necessary light-producing voltage. The bus bar 18 is connected through a suitable voltage source 22 of time varying frequency and a direct current voltage bias source 24 to ground. The other bus bar 18 is connected through a suitable voltage source 26 of time varying frequency to ground. The front electrode 12 is also connected to ground. The sources 22 and 26 are connected to provide two oppositely phased voltages in comparison with the common ground connection. The frequency of the power sources 22 and 26 is of about 10,000 cycles per second. A more detailed description of the bridge circuit is given in my previously mentioned Patent 2,875,380.

The method of fabricating the electroluminescent phosphor or light-producing portion of the screen has been described. As previously pointed out, to attempt to assemble separately a control portion for each lightproducing element would be next to impossible. It is necessary to fabricate the control portions for all the light-producing elements as a single unit or at least a small number of sections. In order to form the control portions for a plurality of the lightproducing elements as a single unit, it is necessary to first form a sheet of nonlinear dielectric material of substantially the same area as the display screen and which has suitable mechanical rigidity. A suitable sheet of nonlinear dielectric material may be of about 10 mils in thickness. To form the dielectric sheet, a quantity of a suitable resin such as melamine formaldehyde is added to water in liquid form. The proportion of such mixture is not critical and 'may, for example, be about twenty-five parts water and one part resin by weight. This mixture is stirred and heated to about 70 C. A suitable nonlinear dielectric such as a ferroelectric material of barium titanate is then added to the solution in powdered form. Fine particles of the order of 3 microns may be used but size is not critical and particles up to 20 microns may be readily used. One part by weight of ferroelectric powder to three parts of the water-resin solution forms a suitable mixture. After thorough stirring, the solution is poured and allowed to settle on a film of polyvinylidene chloride. The film with the deposited mixture'is then heated to about 140 C. and held at that temperature for about one hour in order to evaporate the water and polymerize the resin contained in the mixture. After such treatment, the ferroelectric material and resin material is placed on a slab of zirconia (ZrO or other refractory material of low reactivity. It makes no essential difference whether the film of polyvinylidene chloride is still attached. The zirconia slab is then placed in a furnace where it is heated to about l200-14S0 C. This high temperature causes the resin material to be burned off and results in a strong, dense sheet of the ferroelectric material. Such a sheet is generally called a ferroelectric ceramic sheet 30 and is illustrated in Fig. 2.

Additional information on the preparation of ferroelectric ceramics may be found in an article in the Bulletin of the American Ceramic Society, 33, No. S (May 1954), page 131, Preparation of Reproducible Barium Titanate, by R. M. Callahan and J. F. Murray.

The ceramic sheet 30 of ferroelectric material resulting from the previous treatment should be planar and may be a square six inches on a side and about 10 mils in thickness. The ceramic sheet 30 is next positioned between two electrically conductive layers 32 and 34 of similar area. The layers or sheets 32 and 34 should also be planar and may be of a thickness of about 125 mils. It is necessary to bind the sheets 30, 32 and 34 together into a unitary structure 40. It is necessary to provide a good electrical and mechanical bond between the sheets. One specific method of accomplishing this is by dipping the ceramic sheet 30 into a suitable paint, such as one containing silver particles and a glass frit in a binder of a plastic such as ethyl cellulose in a solvent such as toluol. The paint may also be sprayed or applied by other suitable means. The paint is air dried during which time the solvent evaporates and the binder sets. The treated layer is then heated in air at 750 C. for about thirty minutes and the glass frit becomes molten and reacts with the silver and the ceramic to provide a good mechanical and electrical contact after cooling. It is required to have such a bond in order to withstand the later machining operations. Both sides of the ceramic sheet are then tinned with a suitable solder, such as 36% lead, 62% tin and 2% silver having a melting point of 230' C. The addition of 2% silver to an ordinary lead-tin solder is desirable in order that the silver deposited from the previously applied silver paint will not dissolve into the solder and thus destroy the mechanical bond.

The two sheets 32 and 34 of electrically conductive material which may be of a material such as brass or copper-graphite, are also tinned on one side with a similar solder as that used on the ceramic sheet 30 toassure good contact and the ceramic sheet 30 is then positioned between the tinned surfaces of the brass sheets 32 and 34. The sandwich of the two brass sheets 32 and 34 with the inner ceramic sheet 30 is heated to a temperature of about 230 C. and then is cooled. This melts the solder binding agent and when the solder solidifies bonds the laminated structure 40 consisting of the sheets 30, 32 and 34 into a unitary structure. This is only one suitable process for bonding the laminated structure and other methods may be used which provides a good electrical and physical bond.

The stacked structure 40, shown in Fig. 2, is then placed in a suitable machine 46 for cutting, as illustrated in Fig. 3. The machine 46 illustrated in Fig. 3 shows only a table 44 and a cutting head 48. The stacked structure 40 is positioned on the table and retained a ent thereon by suitable meanssuch as clamps or cement. The cutting head 48 consists of a plurality of cutting wheels of a suitable material such as silicon carbide. The cutting wheels 50 may have a diameter of 2 to 3 inches and a thickness of about 5 to 10 mils. The grooves which are cut in the stacked structure 40, as illustrated in Fig. 4, normally have a thickness of 5 to 10 mils and correspond to the thickness of the wheel 50. The cutting wheels 50 are rotated by a suitable driving means 52, such as an electrical motor. In the normal cutting operation, the grinding wheels 50 will rotate at a speed of about 3500 revolutions per minute. The cutting head 48 may be provided with a sutlicient number of wheels 50 and of such a spacing so as to provide the necessary grooves in one pass. In most cases, it will be necessary to index the machine so that a plurality of passes are made in order to cut grooves in the entire structure 40. In the first operation, the grooves 52, illustrated in Fig. 4, are made by movement of either the cutting head 48 or the table 44 of the machine so that the cuts or grooves 10 mils wide and spaced apart 30 mils are made in one direction and of adepth such that the grooves 52 extend through the conductive layer 32 and the ceramic layer 30, and into the other conductive layer 34. The sandwich 40 is then moved with respect to the cutting head so that additional cuts or grooves 54 are made in the opposite surface of the stacked structure parallel to the grooves 52 in the opposite surface and also spaced intermediate the grooves 52. The grooves 54 are mils in width and also spaced 30 .mils p t It is then necessary to make a plurality of cuts 56 in the same surface as the cuts 52 of similar depth but at 90 with respect to the grooves 52. The cuts 56 are made 30 mils in width and spaced apart 10 mils. The resulting structure is illustrated in Fig. 5. The parallel elements 18 and are electrically conductive bus bars formed from the layer 34. The bridge circuit control elements 62 are connected between bus bars 18 and 20. The element 62 is U-shaped with the end portions 64 of the legs of the U-shaped member formed from the layer 34. A ceramic layer 66 is provided next in each leg which is formed from the ceramic layer 30. The remainder of portion 68 of the element 62 is formed from the layer 32. The portion 68 provides the contact area 70 which is pressed onto the individual areas 16 and retained by a suitable conductive varnish. The conductive varnish also provides a good electrical contact therebetween. in a suitable plastic material as illustrated in Fig. 1.

It is also normally necessary to fill the grooves in the first surface cut with a plastic resin, such as phenolformaldehyde or urea-formaldehyde, in order to improve the mechanical strength of the structure before the grooves are cut in the other side of the structure. It also may be desirable in some cases to space the cutting wheels such that the distance is of the order of mils so that it is necessary to make a second pass to provide the intermediate grooves. This procedure may be necessary in those cases where the structure is extremely fragile.

While I have shown my invention in only one form, it will be obvious to those skilled in the art that it is not so limited but is susceptible of various other changes and modifications without departing from the spirit and scope thereof.

I claim as my invention:

1. In the process of manufacturing a solid state display device, the steps comprising coating a sheet of nonlinear dielectric material with a first material to provide good electrical and mechanical contact and applying thereover a second coating of a solder, placing the treated dielectric sheet between two sheets of electrically conductive material to form a sandwich, heating said sandwich to form an integral body through said solder, and thereafter removing material from one of the exterior surfaces of said The resulting structure is encased in eg a ba t9 te m a p u al qt 18mm endi hrci sh ar elec ic ly soa ust vs s e a the inter edia she t of d s sst' cm ial n m n n h body of the remote electrically condnctive sheet.

2. In the processof manufacturing a solid state display device, the steps comprising coating'both faces of a sheet of nonlinear dielectric material with a heat responsive binding agent, placing the coated sheet between two sheets of electrically conductive material to form a sandwich, heatingsaid sandwich to cause said binding agent to unite said sandwich to form an integral body, and thereafter removingmaterial from the exterior surfaces of said integral body to form'a plurality ofglrooves extending through the electrically conductive sheet and the intermediate sheet of dielectric material, said grooves terminating in the body of the remote electrically conductive sheet.

3.. lnfthe process of manufacturing a solid state disp ay d i e th s e s m is n coating, bo h faces of shee at star n s? d el tri ma r h a heat sponsive binding agent, placing the treated dielectric sheet between two sheets of electrically conductive material to twins laminated st usmra h at s d. laminated structure to cause said binding agent to unite said sheets to form an electrical and mechanical bond, and thereafter u t n a l lit o gr v s in Q9 s f of said am nat d. Structure xtend n th u h h electrically conduc e sh et and. the ie c i sh e n t the remote electrically conductive sheet.

4- I he PI$ of m nufa ur a so State d P y de s e step c mp sin m t n h f c o a n n near d lect ic. ma eri wit a h a responsive binding agent, placing the treated dielectric sheet between two sheets of electrically conductive material to form a laminated structure, heating said laminated structure to cause said binding agent to unite said sheets to form an electrical and physical bond, and thereafter cutting a plurality of grooves in one surface of said laminated structure extending through the conductive sheet and the dielectric sheet into the remote electrically conductive sheet, and cutting a second plurality of grooves in the other surface of said laminated structure extending through the electrically conductive sheet and the dielectric sheet into the remote electrically conductive sheet.

5. In the process of manufacturing a solid state display device, the steps comprising coating both faces of a nonlinear dielectric material with a heat responsive binding agent, placing the treated dielectric sheet between two sheets of electrically conductive material to form a laminated structure, heating said laminated structure to cause said binding agent to unite said sheets to form an electrical and physical bond, and thereafter cutting a plurality of grooves in one surface of said laminated structure extending through the electrically conductive sheet and the dielectric sheet into the remote electrically conductive sheet, cutting a second plurality of grooves in the other surface of said laminated structure extending through the electrically conductive sheet and the dielectric sheet into the remote electrically conductive sheet to form. a control structure and attaching said control structure to an electroluminescent light-producing structure.

6. In the process of manufacturing a solid state display device, the steps comprising placing a nonlinear dielectric sheet between two sheets of electrically conductive material to form a laminated structure, providing a binding agent material between said sheets, heating said laminated structure to cause said binding agent to unite said sheets to form an electrical and physical bond, and thereafter cutting a first group of spaced parallel grooves in one surface of said body extending through the electrically conductive sheet and the dielectric sheet and into' the remote electrically conductive sheet, cutting a second group of grooves in the same surface transverse to said first grooves to provide a plurality of projections on the remote electrically conductive sheet including a portion of said remote sheet, the dielectric sheet and the other electrically conductive sheet, and cutting a third group of grooves in the opposite surface of said body parallel to said first group of grooves to provide a groove spaced between adjacent grooves of said first group.

' 7. In the process of manufacturing a solid state display device, the steps comprising placing a nonlinear dielectric sheet between two sheets of electrically conductive material to form a laminated structure, providing a binding agent material between said sheets, heating said laminated structure to cause said binding agent to unite said sheets to form an electrical and physical bond, and thereafter cutting a plurality of spaced parallel grooves in one surface of said body extending through the electrically conductive sheet and the dielectric sheet-to the remote electr'ically conductive sheet, cutting a plurality of grooves in the same surface transverse to said first grooves to provide a plurality of projections on the remote electricall y -conductive sheet including a portion of said remote sheet, the dielectric sheet and the other electrically conductive sheet, cutting a plurality of grooves in the opposite surface of said body parallel to and alternately spaced with said first grooves for a control structure, providing an electroluminescent layer having a continuous conductive layer on one side and a mosaic of conductive elements on the other side and binding each of said projections on said control structure to one of said conductive elements of said mosaic to provide intimate electrical contact therewith.

8. In the process of manufacturing a storage display structure in which a light display screen of a layer of electroluminescent phosphor is utilized having a continuous conductive coating on one surface of said electroluminescent phosphor layer and a plurality of electrically conductive elements on the other surface of said electroluminescent phosphor layer, the stepscomprising coating both faces ofa sheet of nonlinear dielectric material with a heat responsive binding agent, placing said treated dielectric sheet between two sheets of electrically conductive material to form a laminated structure, heating said laminated structure to cause said binding agent to unite said sheets to form a good electrical and physical ,bond and thereafter removing a first group of grooves of material in one surface; of said laminated structure extending through the electrically conductive sheet and the dielectric sheet into the remote electrically conductive sheet, cutting a second group of grooves in a direction transverse to said first group and in the same surface thereof to provide a plurality of elements similar in number to the number of conductive elements in said plurality of conductive elements on said phosphor layer, and attaching said elements to said conductive elements on said phosphor screen to provide separate controls for each of the light producing elements of the electroluminescent screen.

References Cited in the file of this patent UNITED STATES PATENTS 2,558,019 Toulon June 26, 1951 2,698,915 Piper ..'Jan. 4, 1955 2,792,441 Kazan May 14, 1957 2,818,531 Peek Dec. 31, 1957 

